This invention relates to an apparatus for taking measurements in the ear, having a probe head insertable into the ear canal and an indicating unit. Measuring apparatus of this type which include, for example, infrared radiation thermometers or ear reflectometers, are known in the art.
From WO 98/01730 an infrared thermometer having a visual marking system is known, which enables a user during a temperature measurement to maintain a given distance between the probe head and the object of measurement.
However, the art also knows of infrared radiation thermometers for determining the temperature of a human body, whose probe head which is equipped with a radiation inlet is insertable into the ear canal and capable of measuring the infrared radiation emitted by the tympanic membrane. Considering that blood supply to the tympanic membrane is the same as to the temperature center in the brain, this radiation is representative of the true core temperature of the human body.
Because a difference typically exists between the tympanic temperature to be measured and the temperature of the surrounding ear canal tissue, it is necessary for the probe head to be correctly aligned relative to the tympanic membrane for temperature measurement precision. However, this is not always ensured because bends in the ear canal or frequently occurring natural irregularities (exostoses) may block the free view at the tympanic membrane. Hence the measurement result is appreciably affected by the geometry of the respective ear canal so that more or less significant errors may be introduced. Even a subjectively correct seat of the probe head is no guarantee of a correct alignment to the tympanic membrane, because in the worst case a partial obstruction of the radiation inlet by a skin fold is sufficient to make the measured temperature severely dependent on the direction, producing conventionally an erroneous reading not noticeable by the user with a poor repeatability. When the probe head is accidentally placed directly on the ear canal tissue, errors may also be introduced which pretend an excessively low body temperature.
To solve this problem, it is proposed in U.S. Pat. No. 5,325,863 to provide the user with an audible reply indicative of the quality of positioning. Thus the known ear canal thermometer invariably takes several measurements, and it possesses an audible signal detector delivering a tone as the probe head is inserted in the ear canal whenever the measured temperature value is higher than a previous measurement value. In this arrangement, however, the evaluation of the regions whose temperature is sensed depends on chance, and there is no possibility of checking whether the tympanic membrane as the region with the overall highest temperature has been included in the evaluation and the body core temperature correctly detected. Furthermore, errors introduced due to direct placement of the probe head onto tissue cannot be detected and, accordingly, cannot be corrected either when a measurement is taken.
The problems involved in properly aligning the probe head in the ear canal are precisely the same when the impedance of the tympanic membrane is measured using an ear reflectometer capable of determining accumulations of liquid in the tympanum. To this end, sound waves are emitted at different frequencies, and the sound waves reflected by the tympanic membrane are recorded and evaluated.
It is therefore an object of the present invention to provide an apparatus for taking measurements in the ear, with which erroneous readings due to an insufficient alignment of the probe head to the tympanic membrane can be avoided.
According to the present invention, this object is accomplished by an apparatus having a device for determining the alignment of the probe head in the ear canal.
This device comprises a source of radiation emitting electromagnetic radiation to be passed to the measurement spot targeted by the probe head of the apparatus, a detector responding in the corresponding wavelength region for sensing the radiation scattered by the measurement spot, and an evaluation unit arranged downstream of the detector for determining the alignment of the probe head in the ear canal. The device may further include an indicating unit to represent the alignment.
In a preferred embodiment of an apparatus of the present invention, the source of radiation is a light source emitting energy preferably in the visible region or in the near infrared region, the detector then being a photodetector.
To preclude the effects of the radiation passed into the ear canal on the measurement, the mean intensity of the radiation source is selected suitably low so that in particular heating of the ear canal is prevented. This is accomplishable preferably by the use of a pulsed radiation source and a detector circuit synchronized with it. The power consumption of a pulsed radiation source is less than that of a source which is not pulsed, which presents an advantage particularly where battery-powered apparatus are used. In addition, a pulsed radiation source also enables the radiation background to be determined.
An apparatus of the present invention advantageously includes a first radiation guide, in the above embodiment a light guide, which directs the radiation emitted from the radiation source to the measurement spot, that is, the radiation is given off at the end of the radiation guide close to the measurement spot, radiating into the ear canal. The radiation may be focused or, alternatively, it may form a widening radiation cone. Upon striking tissue, the radiation is reflected diffusely, causing part of it to be passed to the detector either via the same or a second radiation guide. The intensity of the radiation sensed by the detector is dependent on the mean distance between the reflecting tissue and the probe head. Therefore, when the probe head is improperly aligned, a relatively high percentage of the radiation, upon diffusion on the walls of the ear canal, is again coupled in the probe head and sensed in the detector, whilst in the presence of a correct alignment of the probe head to the rear auditory canal and the tympanic membrane, only a minimum amount of radiation is sensed. This enables severe erroneous readings to be detected as they may occur, for example, when the probe head is placed directly onto the tissue.
In the above-described use of two radiation guides, the occurrence of indicating errors due to direct overcoupling of the emitted radiation to the detector is precluded.
In another embodiment of a measuring apparatus of the present invention, the first radiation guide is omitted. In this arrangement the radiation source is disposed at the extreme forward end of the probe head.
To instruct the user with regard to a proper alignment of the probe head, it is possible for the probe head alignment to be indicated visually and/or audibly. For this purpose, the device of the present invention measures the amount of diffuse radiation continuously, that is, preferably as early as the moment when the probe head is inserted into the ear canal. Preferably, the indicating unit comprises a device for producing an audible signal whose volume and/or frequency is/are controlled by the output signal of the detector. Shortly upon inserting the probe head into the auditory canal, the user of an apparatus of the present invention receives a direct reply indicative of the optimum alignment of the probe head to the tympanic membrane or at least to the region of the rear auditory canal. This indication causes the user to align the probe head nearly alike for each measurement, so that good repeatability of the measurement results is obtained.
The indicating unit comprises, for example, a voltage-controlled oscillator driven by the output signal of the detector and having a loudspeaker connected thereto. Any variation of the detected radiant power then effects an increase or decrease in the oscillation frequency and/or oscillation amplitude, so that the user hears a correspondingly changing tone when aligning the thermometer in the ear canal. Proper alignment of the probe head is achieved when the tone with the lowest (or highest) frequency and/or amplitude sounds.
To facilitate a measurement by third persons, another embodiment makes provision for the indicating unit to comprise a visual display, in particular an LED line or a pointer instrument providing the user with a visual indication of the proper alignment of the probe head to the rear auditory canal and to the tympanic membrane. This way of representation enables measurements to be taken on sleeping persons without having to disturb them by an audible signal.
In a preferred embodiment, the evaluation unit of an apparatus of the present invention includes the added provision of a threshold value device which activates the indicating unit for the measurement values and/or the indicating unit for representing the alignment not until the radiant power sensed in the detector has fallen below a predetermined threshold value. This enables the indication of a measurement value to be suppressed until the evaluation unit has sensed a satisfactory alignment of the probe head. Still further, the end of measurement can be indicated to the user when the threshold value is reached. The threshold value is fixed at a level ensuring the requisite measurement accuracy also with differently shaped ear canals.
In a particularly advantageous configuration of the measuring apparatus, the threshold value is adapted to the individual diffusivity of the individual ear canal already the moment when the probe head is inserted into the ear canal. This succeeds particularly well when the user initially moves the probe head to and fro in the ear canal, thereby aligning the probe head in different directions. The threshold value device senses the to-and-fro movement by corresponding fluctuations in the output signal of the detector, and it varies the threshold value when the threshold value is not reached within a predetermined measuring period in spite of this movement.
Wrong manipulation by placing the probe head directly on the tissue is assumed to be the case when the output signal of the detector reaches a correspondingly predetermined second threshold value.
Two preferred embodiments of a measuring apparatus of the present invention involve an infrared radiation thermometer having an infrared sensor, particularly for measuring the temperature of the tympanic membrane, and an ear reflectometer having a sound source and a microphone, in particular for measuring the impedance of the tympanic membrane.
Infrared radiation thermometers known in the art typically include a housing with a radiation inlet for the infrared radiation to be measured, and a waveguide extending from the radiation inlet to the infrared sensor. In an infrared radiation thermometer of the present invention, the waveguide serves the function of conveying both the infrared radiation emitted from the tympanic membrane to the infrared sensor and the radiation source""s radiation reflected in the auditory canal to the detector. Therefore the infrared sensor and the detector are preferably disposed at the end of the waveguide (which hence also assumes the function of the second radiation guide referred to in the foregoing).
In another aspect, provision is made for two separate radiation guides for passing the infrared radiation and the reflected radiation. Alternatively, it is possible for the infrared radiation needing to be measured, for the emitted radiation and the reflected radiation to be guided in a single radiation guide. It is also possible to substitute an optic system having lenses and/or mirrors for the radiation guide(s).
The detector is preferably arranged laterally in the end area of the waveguide in order to minimize its effect on the viewing angle and the sensitivity of the infrared sensor. However, the detector may also be integrated in the housing of the infrared sensor in which case the window material of the sensor housing is selected so that the window is transmissive both to the infrared radiation and in the wavelength region utilized by the radiation source. In a particular configuration, the detector with the infrared sensor is integrated in a microsystem on a chip. Similarly, an integration of infrared sensor, detector and radiation source on a chip or in a housing is also possible.
In an ear reflectometer of the present invention, the detector and the microphone may have a common housing. In a particular configuration, the detector and the microphone are integrated in a microsystem on a chip. Similarly, an integration of microphone, detector and radiation source on a chip or in a housing is also possible.